Electromechanically actuated disc brake system

ABSTRACT

An electromechanically actuated disc brake system for motor vehicles comprising a floating caliper and an actuating unit mounted with the caliper. The actuating unit is an electric motor which, by interpolation of a reducing gear, powers an actuating element, which in turn controls one of two sliding friction linings mounted inside the brake caliper, to interact with the disc brake. With the intent to reduce axial dimensions of the actuating unit, the present invention includes an electric motor with a rotor of ring-shaped design to radially surround the reducing gear.

TECHNICAL FIELD

The invention relates to disc brakes and more particularly relates toactuated disc brake systems for motor vehicles with brake calipers andan actuating unit.

BACKGROUND OF THE INVENTION

A disc brake of this particular type is known from EP-D394 238 B1. Here,the actuating unit consists of an electric motor working with aplanetary gear, and its planetary wheels powering a ring wheel. The ringwheel's rotational motion is transmitted, via bearing elements, to anactuating bush, thus causing its axial displacement or shift which, inreturn, causes the actuating element's respective friction lining tointeract with the disc brake. The electric motor and planetary gear arepositioned side by side in the disc brake's path of actuation. Onedisadvantage of all known, electromechanically actuated, disc brakes isthe considerable axial extension of the actuating unit.

It is the intent of the submitted invention to improve on anelectromechanical disc brake of the type mentioned above, with specialemphasis put on reducing the axial dimensions of the actuatingmechanism.

Its conceptual problem is solved in that the electric motor's rotor isof ring-shaped design, radially surrounding the reducing gear. Thefunctionality of such an electromechanically actuated disc brake isunique in its strong dynamics of brake actuation and extremely compactdesign, allowing the transmission of high-density, mass-intensivebraking power.

Practical application of the invention calls for the reducing gear to bea threaded roller pinion, with its threaded nut transmitting power tothe rotor. An economically advantageous refinement has the threadedroller pinion designed as one featuring axial return of the rollers. Itis of special convenience to have the actuating element represented bythe spindle of the threaded roller pinion.

In order to achieve a considerable reduction in the electric motor'srequired torque, the power exchange between rotor and threaded nut isconducted by means of a planetary gear, with its sun wheel deployed atthe rotor, while the planetary wheels are located at the threaded nut.The internal toothing of the brake calipers represents the hollow wheelof the planetary gears, interacting with the planetary wheels. It is ofadvantage to have available, between rotor and gear nut, a needlebearing and ball bearing configuration, under which the radial externaltrack of the ball bearing is situated in the rotor and the radialinternal track is, at least partially, situated in the threaded nut.Such arrangement makes possible a reduction in electric waste and anenlargement of the rotor's angle--quite advantageous for deployment ofthe threaded spindle as a requirement for the lining's positioning.

The smooth transmission of the electric motor's actuating power isachieved through cooperation of the spindle with a power transmissionplate which is installed on the direct-actuated side of the frictionlining.

A substantial reduction in efficiency loss, due to friction beingpresent in the threaded roller pinion, is realized by installing aplunger rod (or pressure bar) between the threaded spindle and powertransmission plate.

An even transmission of compressive forces between threaded spindle andpower transmission plate is achieved by partially installing the plungerrod inside the threaded spindle, and securing it by way of two sphericalcaps. The first of these is intended to be mounted in the threadedspindle, with the other on the axial extension of the power transmissionplate. Ideally, the first of the spherical caps should be mounted at thecenter point of the threaded spindle's axial length, and/or within thespace defined by the spindle's thread rollers.

A further characteristic is the establishment of a connection oftorsional strength between thread spindle and the power transmissionplate, allowing smooth transmission of torsional momentum resulting frombrake application force. It is achieved through the deployment of ametallic bellows between the threaded spindle and power transmissionplate, which is placed coaxially to the plunger rod, and firmly attachedto the threaded spindle and power transmission plate, preferably bywelding.

The electric motor's hollow shaft, integrated in the actuating unit, isoptimally positioned because the screw threaded nut exhibits radialexpansion, enabling it to be supported by a radial bearing (it beingdesigned as a cross shaft bearing and/or four-point bearing). Thebearing's inner ring should be determined by the circumferentialdimension of the expansion. Its ability to absorb high axial and radialforces and stalls or lock-ups adds to a further stabilization of thehollow shaft.

The electric motor has the versatility to operate as either a permanentmagneto-excited, electronically commutating electric motor (torque), ora connected reluctance motor (SR).

The mentioned motor types are especially suitable for generating hightorque when in standstill mode.

To find a good location for placement of the rotor, particularly underutilization of the mentioned torque motors, the invention provides for acontact-free resolver (angle indicator), which works in concert with thereducing gear and pinpoints the actuating element's location. Theresolver may be made up of two rings with electric windings, spaced byan air gap. One of the rings, preferably the radial inner ring, shouldbe firmly attached to the rotor, while the other is installed in thehousing, with torsional strength intact. Such a resolver affords highdefinition; hence, a targeted braking process of optimal incrementseases the precise positioning of the friction lining.

The resolver's initial signal can at the same time be used forcommutation of the torque motor.

Another characteristic variation of the concept is available, whereby areadjusting spring is inserted between the screw thread nut and thespindle which, following the rotational motion, allows the thread nut acounter-rotational motion step. The feature prevents the brake to remainin its actuated state, brought about by its own hysteresis, e.g. afterpower failure. The remaining brake impulses are essentially eliminated.

Another characteristic is the presence of a torsion retainer/equalizer,located between the power transmission plate and the first frictionlining. For example, the deployment of a lining support spring,installed on hydraulic-actuated disc brakes with friction lining, canserve as a torsion retainer.

To ensure confirmation of contact between the friction lining and discbrake, contact sensor pins are embedded in the friction lining tomeasure electric resistance between the disc and lining. They furtherserve the purpose of monitoring the lining's wear and tear.

To effectively protect the actuating mechanism from soilage, likesplashing water, an elastic sealer element is located between thehousing and actuating element (spindle).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A cross section of the first embodiment of theelectromechanically actuated disc brake of the present invention.

FIG. 2 Complementary to FIG. 1, a second version of the subject.

FIGS. 3,4,5 The third, fourth, and fifth versions of the subject,complementary to FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now referring to FIG. 1 which shows the disc brake as a floating caliperdisc brake. It is composed essentially of a sliding caliper 1, mountedin a rigid frame (not shown here) and an actuating unit 2, with itshousing 8 attached to caliper 1 (again, mounts not shown). A set offriction linings 4 and 5 one positioned on caliper 1 in a manner so asto be in juxtaposition to the left and right flat surfaces of disc brake3.

Subsequent descriptions will refer to friction lining 4, shown right inthe drawing, as first friction lining, with friction lining 5 designatedsecond.

While contact of friction lining 4 with disc brake 3 is under directcontrol of actuating unit 2 and its actuating element 30, the reactivepressure forces springing from actuation of brake caliper 1, will causelining 5 to press against the opposite surface of brake disc 3.

The previously mentioned actuating unit 2 is composed of an electricmotor 6, which in the example is represented as a permanentmagneto-excited, electronically commutating (torque) motor, with stator9 rigidly fixed in housing 8 and rotor 10 (or hollow shaft) being fermedby ring-shaped support 28 which is equipped with several permanentmagneto-segments 29. Between torque motor 6 and above mentionedactuating element 30 (preferably deployed coaxially to motor 6), areducing gear is positioned. It is displayed in the example as threadedroller pinion 11 and 14, and consists of a screw threaded nut 11 and athreaded spindle 14. Parallel axis threaded rollers 12 and 13 arearranged in threaded nut 11. The threaded rollers will, duringrotational motion of threading nut 11, rotate in planetary mode withoutaxial shift, and will set in axial motion the threaded spindle 14.Radial guidance of threaded rollers 12 and 13 is assured by two guidedisks 40, located at the ends of threaded rollers 12 and 13, and toothedwheel rims (not shown).

The mentioned actuating unit 2 consists of electric motor 6, shown inthe example as permanent magneto-excited, electronically commutating(torque) motor, with its stator rigidly fixed in housing 8. Its rotor 10and/or hollow shaft is formed by a ring-shaped support 28, equipped withseveral permanent magneto-segments 29. Between torque motor 6 andpreviously mentioned actuating element 30 (preferably arranged incoaxial fashion to motor 6), a reducing gear is installed, which isdisplayed as threaded roller pinion 11 to 14. The threaded roller pinion7 consists of a threaded nut 11 and a threaded spindle 14, within whichthreaded unit 11 is axially parallel to threaded rollers 12,13. Thesewill, during rotational motion of threaded nut 11, rotate in planetaryfashion without axial shift and will set in axial motion threadedspindle 14. Two guidance discs 40 are arrayed at the ends of threadedrollers 12,13 to provide radial guidance. The additional toothed wheelrims are not shown.

The most suitable arrangement has rotor 10 of torque motor 6 connectedunder torsional strength to threaded nut 11 by inclusion of a featherkey 39. Threaded spindle 14 constitutes actuating element 30, whichunder assistance of power transmission plate 24 actuates the firstfriction lining 4. A torsion retainer 25 is preferably inserted betweenpower transmission plate 24 and the first friction lining 4. Torsionretainer 25 consists of a pin embedded in friction lining 4, and willplug into an inlet allowed for in power transmission plate 24. A radialbearing supported by caliper 1 controls reducing gear 7 and hollow shaftor rotor 10. The radial bearing in the example shown is a cross rollerbearing 16. It consists of a bearing's external ring 18 (shown in FIG. 1in divided form), a bearing's internal ring arrayed on a collar-shapedradial expansion 15 of threaded nut 11, and several cylinder rollers 19arrayed between bearing rings 17,18. The bearing rings 17,18 form fourinterconnected tracks, showing at a 45° pitch relative to the bearinglevel, and/or two sets of twin tracks, offset by 90°, where cylinderrollers 19 (in X-arrangement) alternately roll off on one of the twintracks.

Because the used cross roller bearing can handle any combination ofaxial, radial, and stalled loads, a second bearing is redundant.

A four-point bearing may replace a cross roller.

To position threaded roller pinion 7 exactly and control signals forelectronic commutation of torque motor 6, housing 8 in actuating unit 2contains a resolver 20.

In the given example, a resolver consists of two coaxial rings 21,22,which are equipped with electric windings and are spaced by an air gap.The radial internal ring 21 is linked to threaded nut 11 by means of anintermediate member 61 while the other ring 22 is installed fortorsional strength in housing 8.

For the purpose of clearly recognizing contact between friction linings4,5 and brake disc 3, the former have been equipped with contact pins26. The interior of housing 8 is protected by a cover 31, located nearbyresolver 20, and is additionally protected by an elastic, membrane-likesealer 27 to guard against soilage from splashing water. Sealer 27 isbest inserted between actuating unit 30 or threaded spindle 14, and aretaining ring 32, axially positioned on the bearing's external ring 18.

To dissipate generated heat of torque motor 6 operations, housing 8 isequipped with large-scale cooling ribs 33.

The embodiment of FIG. 2 shows the actuating unit 2 being powered by aconnected reluctance motor (SR-motor). The bearing's internal ring orthe radial interior twin tracks of mentioned cross roller bearing isformed by the circumferential dimension of expansion 15 of threaded nut11. Because of its single-piece design, the internal bearing ring withthreaded nut 11 is of higher operating precision, and less installationis involved, with modular assembly possible. The reducing gear 7 is, inFIG. 2, displayed as a threaded roller pinion with axial return ofrollers 34, which are positioned in a cage 35, holding them parallel tothreaded spindle 14 and equidistant to the spindle's circumference. Thethreaded rollers 34 conclude their circuit to arrive at an axial nut(not shown) inside threaded nut 11 to separate from both threaded nut 11and the spindle's thread. The axial return of rollers 34 to theiroriginal position is controlled by cams (not shown) inside the nut'sthread. Rotor 10 of the SR motor is made up of several ring-shaped rotormetal units 36, attached across on threaded nut 11, and interlocking fortorsional strength. The second version of the invention's SR motor isresistant to higher temperatures, which eliminates the need for coolingribs on housing 8 of actuating unit 2.

To prevent remaining brake momentum, after the act of braking, to affectthe wheel if a failure of control electronics occurs through hysteresisof the actuating unit, a spiral-shaped readjusting spring 23 is providedwhich installs between threaded nut 11 and a cover, closing off themotor housing. The readjusting spring moves the threaded nut 11 counterto the actuated rotational direction, enabling friction linings 4,5 tolift off brake disc 3. For uniform initiation of actuating forces onfriction linings 4,5 in housing 8 of the actuating unit, caliper 1 mustbe massively dimensioned. To reduce flexural impact of friction linings4,5 on housing 8 of actuating unit 2, it is recommended to designcaliper 1 as a framed caliper. Thus, only pulling forces enter thehousing, without imposing flexural tension within the support base ofactuating unit's 2 bearing.

The invention's third embodiment demonstrates the transmission ofpressure forces between threaded spindle 14 and power transmission plate24 via threaded spindle 14, partially located inside plunger rod 41, andbeing mounted in two spherical caps 42. The first is positioned at thecenter of threaded spindle's 14 axial length (between threaded rollers12,13) while the second spherical cap 43, being nearer to frictionlining 4 rests in the axial extension 44 of power transmission plate 24.Furthermore, between power transmission plate 24 and/or its extension 44and threaded spindle 14, a metallic bellows 45 is welded to both parts,which provides a connection of torsional strength for transmission oftorsional momentum, resulting from the brake application forcesgenerated by the threaded spindle.

Now referring to FIG. 4, a reduction of the required motor momentum isachieved in the fourth embodiment of the present invention by purposefulintegration of a planetary gear 46,47,48,49. Deployed most effectivelybetween rotor 10 and threaded nut 11, the planetary gear consists of asun wheel 46, formed on rotor 10 in external toothed arrangement 55,several planetary wheels (two of them depicted with reference numbers 47& 48) and a hollow wheel 49, formed by internal toothing 50 incaliper 1. The mounting of the rotor 10 on threaded nut 11 takes placeby combination of a schematic needle bearing 51 and a ball bearing 52,with its radial external track 53 contained in rotor 10, while itsinternal track 54 is laid out partially at the end of threaded nut 11,and partially on bush 60. This facilitates the selection of a spindlethread with steeper pitch for greater effect.

OPERATION OF THE DEVICE

When the stator 9 is excited, the rotor 10 starts rotating. Presumingthe direction of the stator's rotation be counterclockwise in a viewfrom the right side of the drawing. Then the lower part of the rotor 10moves into the plane of the picture, while the upper part moves out ofthe picture plane. With its external toothed arrangement 55, the rotorengages the planetary wheels 47 and 48 which consequently rotate in aclockwise direction. Thus, they move along the internal toothing 50 ofthe static hollow wheel 49 in a counterclockwise direction. Since theaxles of the planetary wheels 47 and 48 are born on the collar-shapedradial extension 15 of the threaded nut 11, the threaded nut 11 willrotate along with the planetary wheel axles in a counterclockwisedirection. This causes the threaded rollers 12 and 13 to rotatecounterclockwise as well. The threaded rollers 12 and 13 are providedwith right-hand threads which, during a counterclockwise rotation, shiftthe threaded spindle 14 to the left, for it is secured against rotation.In this way, brake lining 4 is brought into contact with the brake disc,while brake lining 5 is pressed against the brake disc by reactivepressure forces as described in connection with FIG. 1. The brakelinings are released by a clockwise rotation of the rotor 10.

FIG. 5 of the drawing demonstrates the invention's fifth embodiment,when electric motor 6 is designed as an externally operating motor. Inthe next example shown, the electric motor's 6 stator 90 is fusedlocally to cylindrical part 56 in housing 8. Operating heat is releasedvia part 56 to housing 86. Rotor 100, enclosing stator 90, is linked tothreaded nut 11 per bell-shaped flange 57, and thus mounted on the sameside. To assure utilization of even small air gaps between rotor 100 andstator 90, the rotor 100 on the drawing's right side is mounted with aradial bearing 58 in housing 8, which by use of a (Belleville) springwasher 59 finds axial support on housing 8.

We claim:
 1. An electromechanically actuated disc brake system for motorvehicles including a caliper and an actuating unit attached to thecaliper, wherein the caliper is adapted to engage two friction linings,each interacting with a respective disc surface, wherein one of thefriction linings is direct-controlled by an actuating element,comprising:an electric motor, mounted coaxially to the actuatingelement, and a reducing gear assembly, mounted between the electricmotor and the actuating element wherein the electric motor includes aring-shaped rotor which surrounds the reducing gear assembly in radialfashion, wherein the reducing gear assembly is designed as a threadedroller pinion having a threaded nut linked to the rotor for the purposeof power transmission which is executed via a planetary sear assembly,with a needle bearing and a ball bearing located between the rotor andthe threaded nut, each bearing having an internal and an external radialtrack, wherein the ball bearing's external radial track is defined inthe rotor, and its internal radial track is partially defined in thethreaded nut.
 2. An electromechanically actuated disc brake system,according to claim 1, wherein the threaded nut includes a radialexpansion to facilitate its support on a radial bearing.
 3. Anelectromechanically actuated disc brake system, according to claim 2,wherein the radial bearing is designed as a cross roller bearing.
 4. Anelectromechanically actuated disc brake system, according to claim3,wherein the radial expansion of the threaded nut accommodates aninternal ring of the radial bearing.
 5. An electromechanically actuateddisc brake system, according to claim 2, wherein the radial bearing isdesigned as a 4-point bearing.
 6. An electromechanically actuated discbrake system, according to claim 1, wherein the actuating element isformed by a spindle of the threaded roller pinion.
 7. Anelectromechanically actuated disc brake system, according to claim 6,wherein the spindle operates in concert with a power transmission plategoverning the functions of the direct-controlled friction lining.
 8. Anelectromechanically actuated disc brake system, according to claim 6,wherein the spindle includes a radial keyway on its side, facing thefriction lining.
 9. An electromechanically actuated disc brake system,according to claim 1, further including a resolver working together withthe reducing gear for the purpose of monitoring the actuating element'sposition.
 10. An electromechanically actuated disc brake system,according to claim 9, wherein the resolver consists of an internal ringand an external ring, each with electric winding and spaced from eachother by an air gap, with the internal ring firmly connected to therotor, and the external ring connected to a housing accomodating theactuating unit.
 11. An electromechanically actuated disc brake system,according to claim 1, wherein the threaded roller pinion is designed asa threaded roller pinion with means for axial return.
 12. Anelectromechanically actuated disc brake system, according to claim 1,wherein the planetary gear assembly includes a sunwheel, a plurality ofplanetary wheels, and an internally toothed hollow wheel, and the sunwheel is positioned at the rotor, while the planetary wheels areattached to the threaded nut, interacting with the internal toothing ofthe hollow wheel.
 13. An electromechanically actuated disc brake system,according to claim 1, wherein the electric motor is designed as anexternally operating motor, with a stator firmly attached to thecaliper.
 14. An electromechanically actuated disc brake system,according to claim 1, wherein the electric motor is designed as apermanent magneto-excited, electronically commutating electric motor.15. An electromechanically actuated disc brake system, according toclaim 1, wherein the electric motor is designed as a connectedreluctance motor.